Accessory Structures in Honolulu, HI: What Residents Actually Need to Know

If you live in Honolulu or are thinking about moving there, accessory structures are one of those things you probably won't think about until they affect you directly. Honolulu has 8 specific rules on the books covering different aspects of accessory structures, and some of them might surprise you.

Carport Rules

Honolulu carports must meet the same Land Use Ordinance (LUO) yard setbacks as the main house unless the homeowner obtains a Zoning Adjustment under ROH §21-2.140-1. A one- or two-car carport may encroach into required front and side yards only if no other viable alternative exists relative to a dwelling legally built before October 22, 1986, or to lot topography, and the carport's horizontal footprint generally cannot exceed 20 feet by 20 feet. A DPP building permit under ROH Chapter 16 is required, and carports do not count as floor area for FAR purposes.

Key details: Code Sections: ROH §21-2.140-1 (LUO); ROH Ch. 16 (Building Code). Standard Setbacks (R-5): 10 ft front, 5 ft sides, 5 ft rear. Encroachment Allowed: 1- or 2-car carport, with adjustment. Pre-1986 Dwelling Required: Yes, for yard encroachment. Max Footprint (adjustment): 20 ft x 20 ft.

Building or expanding a carport without the required DPP building permit is a violation of ROH Chapter 16 and §21-2.140-1, with penalties including a stop-work order, removal of the structure, and after-the-fact permit fees that are doubled (so $1,200 for the carport adjustment alone). Encroaching into a required yard without an approved zoning adjustment is a separate LUO violation under ROH §21-2.10 and can carry civil fines of up to $1,000 per violation, plus additional per-day fines for ongoing non-compliance. Converting a permitted carport to enclosed living, storage, or business space without obtaining a new permit and meeting LUO floor-area, setback, and parking standards is a frequent source of citations. Owners who have built without permits and are then cited must pay the doubled application fees and submit the surveyor-certified site plan, but payment of the fee does not relieve the owner from compliance with the LUO or from related penalties.

Shed Rules

Honolulu allows one-story detached storage sheds of up to 120 square feet on residential lots without a building permit under ROH Ch. 18. Larger structures require a building permit and must conform to zoning setbacks under ROH Ch. 21.

Key details: Permit-exempt size: Up to 120 sq ft (one story). Typical side/rear setback: 5 feet (residential). Permit required above: 120 sq ft aggregate. Governing code: ROH §§ 18-3.1 & Ch. 21 LUO.

Building without a required permit may result in stop-work orders, fines, and mandatory removal. Zoning violations are subject to DPP enforcement action.

Honolulu is more permissive than most cities when it comes to shed rules. That said, there are still limits.

Garage Conversions

Honolulu's LUO § 21-5.720 allows garage and accessory structure conversions into accessory dwelling units in residential zones, subject to floor area limits, parking requirements, and a building permit from DPP.

Key details: Minimum lot size: 3,500 sq ft. Max ADU size (small lot): 400 sq ft (3,500–4,999 sq ft lot). Parking requirement: 1 space per ADU (may be waived). Transit waiver radius: Within 0.5 mile of rail station. Governing section: LUO § 21-5.720.

Unpermitted conversions subject to stop-work orders, fines, and mandatory removal. DPP enforces under ROH Ch. 16 (Building Code) and LUO Ch. 21.

ADU Rules

Honolulu allows one accessory dwelling unit on residential lots of 3,500 sq ft or more. Size is capped at 400–800 sq ft depending on lot size. Owner must live on the property and ADUs may only be rented long-term (six-month minimum).

Key details: Minimum lot size: 3,500 sq ft. Max ADU size (small lot): 400 sq ft (3,500–4,999 sq ft lot). Max ADU size (large lot): 800 sq ft (5,000+ sq ft lot). Minimum rental term: 6 months (180 days). Owner occupancy required: Yes — main house or ADU.

Violation of the owner-occupancy covenant or the long-term rental requirement is enforceable by the Director of Planning and Permitting under ROH §§ 21-2.150 et seq., including fines and orders to cease unpermitted use.

ADU Rental Restrictions

Honolulu prohibits short-term rentals (under 90 days outside resort districts, under 30 days in resort districts) of Bill 7 ADUs under both the recorded long-term rental covenant in LUO Sec. 21-5.730 and Bill 89 (2019) / Bill 41 (2022) STR enforcement. ADUs must be rented for 180 days or longer per the recorded covenant. Hawaii state General Excise Tax (GET) and Transient Accommodations Tax (TAT) apply to rentals.

Key details: Min Lease for ADU: 180 days (recorded covenant). Citywide STR Floor: 90 days (Bill 41). STR Fine: Up to $10,000/day. GET Rate (Oahu): 4.712%. TAT Rate: 10.25% state + 3% Oahu.

Renting a Bill 7 ADU shorter than 180 days violates the recorded covenant and triggers daily civil fines, listing removal orders, and revocation of the ADU permit. Bill 89/Bill 41 STR violations carry fines up to $10,000 per day under ROH Sec. 21-2.150. Failure to remit GET or TAT triggers Hawaii Department of Taxation penalties and interest.

Compared to other cities, Honolulu takes a harder line on adu rental restrictions. The enforcement and penalty structure reflects that.

ADU Permits

Honolulu City and County recognizes two distinct accessory residential units under the Land Use Ordinance (LUO) Chapter 21: the traditional Ohana Dwelling Unit (LUO Sec. 21-5.700) and the Accessory Dwelling Unit (ADU) created by Bill 7 (2015) under LUO Sec. 21-5.730. Both require a building permit through the Department of Planning and Permitting (DPP). Lot size, infrastructure, and zoning eligibility differ between the two.

Key details: Code Authority: LUO Chapter 21. Ohana Unit: LUO Sec. 21-5.700. Bill 7 ADU: LUO Sec. 21-5.730. Min Lot for ADU: 3,500 sq ft. Max ADU Size: 800-1,000 sq ft.

Constructing an Ohana or ADU without permits violates LUO Sec. 21-2.30 and Revised Ordinances of Honolulu Chapter 16 (Building Code), triggering Notice of Violation, daily civil fines up to $1,000 per day under ROH Chapter 21-2.150, stop-work orders, and required removal or restoration. Using a Bill 7 ADU as a short-term rental violates the recorded long-term rental covenant and triggers separate Bill 89 enforcement.

ADU Impact Fees

Honolulu does not impose a dedicated ADU impact fee, but Board of Water Supply (BWS) Water System Facilities Charges and Department of Facility Maintenance sewer assessment fees commonly add several thousand dollars per ADU. Standard DPP building permit fees scale to construction valuation. Bill 7 ADU applicants also pay a per-unit infrastructure assessment.

Key details: Dedicated ADU Impact Fee: None. Sewer SFC: ~$4,500-$5,000 per unit. BWS WSFC: Several thousand per DUE. Building Permit: $40-$60 per $1,000 valuation. School Impact Fee: Not authorized in HI.

Failure to pay BWS or sewer connection fees prevents service activation. Unpaid DPP fees prevent permit issuance. Hooking up to water or sewer without authorization violates ROH Chapter 14 and triggers fines plus disconnection. Skipping permits and fees triggers back-permit fees with double-fee penalties under ROH Chapter 18.

ADU Owner Occupancy

Bill 7 ADUs in Honolulu (LUO Sec. 21-5.730) require a recorded covenant restricting use to long-term residential rental (180+ day leases) but do not require owner occupancy of the principal dwelling. Traditional Ohana units (LUO Sec. 21-5.700) historically were intended for extended family but the LUO does not impose a formal owner-occupancy mandate on Ohana units either.

Key details: Owner Occupancy Required: No (city law). Bill 7 ADU Covenant: 180+ day rentals only. Ohana Restriction: Family use originally intended. Separate Sale: Not allowed (single lot). HOA Authority: HRS 421J / 514B.

Operating a Bill 7 ADU outside long-term rental terms violates the recorded covenant and triggers Notice of Violation, daily civil fines under LUO Sec. 21-2.150, and Bill 89 STR enforcement (fines up to $10,000 per day). Selling an ADU separately from the principal dwelling violates LUO single-lot requirements. HOA covenant violations are enforced civilly per community documents.

The Bottom Line

Honolulu's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Honolulu is broadly strict or permissive.

All of the above reflects Honolulu's municipal code as of our last review. If you need specifics on fines, exemptions, or filing requirements, the detailed ordinance pages linked above have the full breakdown.